As exciting as it can be to track which shares have skyrocketed in price, it can also be worthwhile keeping an eye on which stocks aren’t performing so well.

In many instances, it is advisable to avoid so-called “falling knives” which may be fundamentally flawed or else operate in a struggling industry. In other situations, however, plunging share prices can also represent opportunities.

Below are the five worst performing shares from the ASX 200 index over the last 30 days, based on figures from S&P Global Market Intelligence, and reasons why they may have fallen so sharply:

TPG Telecom Ltd (ASX: TPM)

TPG Telecom shares have shed nearly a third of their value over the past 30 days. They’re down 32.8% – and 2.7% today alone – following a lacklustre earnings report that was recently released. While TPG recorded substantial growth in the 2016 financial year, much of that was from acquisitions with little organic growth forecast for the 2017 (current) financial year.

Vocus Communications Limited (ASX: VOC)

Vocus Communications, another telecommunications business, has also fallen 20% over the last 30 days. It’s likely that the mild growth forecast by TPG Telecom has impacted investor expectations for the wider industry, which would partially explain Vocus’ fall. It’s also possible that investors are concerned about Vocus’ ability to integrate its various recent acquisitions into the business, as well as the sudden resignation of its Chief Financial Officer.

OFX Group Ltd (ASX: OFX)

Formerly OzForex Group, OFX Group has plunged 18.9% over the month to $1.86. Although there has been some director buying, which is a positive sign for the group’s shares, Macquarie also cut its price target on the currency exchange company by 12% to $2.30 recently. The risk of greater competition in the sector could be weighing on investor sentiment for the shares.

Macquarie Atlas Roads Limited (ASX: MQA)

This company is a global toll road developer and operator. Its shares have fallen 5% today alone to $4.63 and are down 12.1% in the past month after Macquarie Group Ltd (ASX: MQG) completed a selldown of a portion of its stake in the company. Macquarie Atlas Roads’ shares have now fallen 23% since peaking at $6 in mid-August.

Santos Ltd (ASX: STO)

Santos operates in the energy sector and has thus been hit hard in recent years by a plunging oil price. Its shares did recover somewhat between mid-January and mid-August, but have fallen sharply again since then. They’re down roughly 11.6% in the last month.

Is there an opportunity?

The companies that stand out the most to me here are both TPG Telecom and Vocus Communications. The pair have been savagely sold off in recent times on signs Australia’s telecommunications industry may finally be maturing, following years of above-average growth.

Whether that represents an opportunity is up to each individual investor. There is no doubting that both represent great businesses that could be worth an investment after their recent falls. That said, if growth really has slowed to a trickle, then both shares could also still be somewhat expensive.

Investors who believe the selloff has been overdone could certainly look to buy. Other investors who are less tolerant to risk may want to hold off at least until their next set of earnings results are released, which could provide further indication of the direction of the industry.

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Motley Fool contributor Ryan Newman has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.